Monopropellant composition including hydroxylamine perchlorate

ABSTRACT

A GELLED LIQUID MONOPROPELLANT COMPRISING AN AQUEOUS SOLUTION OF A MIXTURE OF OXIDANTS SUCH AS SODIUM PERCHLORATE AND HYDROXYLAMMONIUM PERCHLORATE, A FUEL SUCH AS BORON, POWDER AND A GELLING AGENT SUCH AS SILICA GEL.

United States Patent Ofiice represented by the Secretary of the Navy No Drawing. Filed July 8, 1969, Ser. No. 843,908

Int. Cl. C06d /06 US. Cl. 149-22 15 Claims ABSTRACT OF THE DISCLOSURE .as boron, powder and a gelling agent such as silica gel.

BACKGROUND OF THE INVENTION This invention relates generally to liquid monopropellant compositions and more particularly to a gelled liquid monopropellant composition especially useful for underwater propulsion of ordnance vehicles, gas generators and other applications.

The simplest type of propellant system is the liquid monopropellant which basically comprises either an oxidized dissolved or suspended in a fuel (or vice versa), or a liquid solution in which all of the oxidizer and fuel necessary for combustion is combined in a single molecule. Generally, liquid type monopropellants are perferred over other compositions because of their high degree of thrust control and because of the simplicity of the feed system necessary to feed the composition to the combustion chamber of the reaction motor; there being required only a single pump, a single storage tank and a single feed line. Presently, however, the state of the art liquid monopropellants are generally inadequate for such military applications as torpedo propulsion and underwater gas generators since a great portion of their combustion products such as methane, and nitrogen oxides cannot be considered water soluble. Insoluble products are deleterious to military operations because they are the prime cause of surface wake which facilitates enemy detection of the underwater vehicle. The Wake also tends to interfere with both the noise-sensitive sonar homing device within the torpedo and with the detection devices on the launching submarine. Furthermore, a wake does not allow the use of back pressure reducing devices Which aid to increase the depth performance of the torpedo.

Another problem with conventional liquid monopropellant compositions is that the substantial increase in the performance of modern ships and submarines in recent years has increased military demands for greater range, depth and speed which properties necessitate compositions having greater energetics than those obtainable from presently available propellants.

It is therefore desirable to obtain a liquid monopropellant which can generate a high percentage of water soluble combustion products yet which is characterized by high energetics capabilities.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a new liquid monopropellant which generates a high percentage of Water soluble gases on combustion.

It is also an object of this invention to provide a liquid monopropellant having greater energetics than those previously available.

It is a further object of this invention to provide a liquid monopropellant which is especially suited for underwater propulsion applications.

3,730,789 Patented May 1,, 1973 These and other objects are accomplished by providing a gelled liquid monopropellant which comprises an aqueous solution of a mixture of water soluble oxidizers, a water insoluble but compatible fuel, and a compatible gelling agent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel monopropellants of this invention are prepared by forming a water solution of a mixture of oxidizers such as sodium perchlorate and hydroxylammonium perchlorate (HAP), adding thereto a water insoluble fuel, such as boron in finely divided form, with the further addition of a gelling agent, such as silica gel, wherein said total mixture of oxidizers, water, fuel and gelling agent are present in the weight ratio of about 7: l :0.5:.007 to about 1:728:05.

It is believed that the water acts in the present composition as a desensitizing agent for the oxidants employed. It is also believed that the water provides the necessary cooling to control the flame temperature of the combustion reaction. For these purposes and also for the purpose of dissolving the oxidants it is desirable to use water in an amount sufiicient to provide a total oxidizer to water Weight ratio of about 7:1 to about 1:7, but preferably a ratio of about 5:3 is employed.

For the purposes of this invention a large number of water soluble oxidizers are operable herein. For example, the preferred oxidizing mixture of sodium perchlorate and hydroxylammonium perchlorate (HAP) may be replaced by mixtures wherein the sodium perchlorate is substituted for by other water soluble oxidizers such as metal chlorates, metal perchlorates, and organic alkyl and aryl ammonium perchlorates and the HAP is replaced by other water soluble substituted hydroxylammonium perchlorates. Specifically some of these other water soluble oxidizers are, e.g., lithium chlorate, sodium chlorate, magnesium chlorate, aluminum chlorate, lithium perchlorate, magnesium perchlorate, potassium perchlorate, aluminum perchlorate, ammonium perchlorate, methylammonium perchlorate, methylene diammonium diperchlorate, ethylene diammonium diperchlorate, aniline perchlorate, N- methyl hydroxylammonium perchlorate, N'ethyl hydroxylammonium perchlorate, O-methyl hydroxylammonium perchlorate, O-ethy-l hydroxylammonium perchlorate and the like. The proportions of the two oxidizing salts of the total oxidant mixture may vary Within a wide range, but for optimum results about 1 part by weight of the hydroxylammonium salt employed for about every 4 parts by weight of the other oxidizing salt is used.

The quantity of the fuel used in the propellant composition of the present invention is not critical and is dependent generally on the percentage of insoluble exhaust products which can be tolerated for a given application. The more closely the quantity of fuel and oxidant approximates the stoichiometric balance, the greater the percentage of water soluble exhaust products will be pro vided. In general, sufficient fuel should be present to provide the weight ratio of total oxidant to fuel of from about 12:1 to 1:8. The fuel substances of the present invention are employed in finely divided form and although the preferred material is boron powder, any substance which is compatible with the system and which forms mainly gaseous or liquid, water soluble or condensable combustion products may be used. Some of these other fuels include boron carbide, sulfur and phosphorus.

A large number of gelling agents are operable herein for the purposes of this invention. Although the preferred gelling agent is silica gel other gelling agents such as inorganic or organic polymers may be utilized. Specifically some other operable gelling agents are polymeric boratozirconium chloride, polymeric glyceratozirconium chloride, polyacrylic acid, polyacrylic acid cross-linked with divinyl benzene, polyacrylamide and polyacrylamide crosslinked with divinyl ether. The amount of gelling agent employed is not critical and is merely enough to keep the solid fuel in suspension. The gelling agent may range from about 0.05 percent by weight to about percent by weight of the total composition, but preferably is employed from about 0.5 percent to about 3 percent by Weight of the total composition.

Many additives may be added to this composition to modify its property without departing from the present invention. For example, various stabilizers may be included such as ethylenediaminetetracetic acid, the salts thereof and similar complexing agents.

The composition as hereindescribed will provide up to 98 percent of water soluble or condensable combustion products, thereby rendering the composition especially suited for underwater propulsion Where minimium wake characteristics are required. Morover, this high amount of water soluble exhaust products makes the application of back pressure reducing devices possible, which increases the performance of a torpedo at deep depths considerably.

The compositions of this invention are also characterized by the additional desirable properties of long storage stability, low sensitivity to shock, non-flammability under ambient conditions and nontoxicity. Another advantage is that the present composition has a higher energy content than conventional fuels as measured on either a weight or a volume basis.

Having generally described the invention the following examples are given for purposes of illustration. It will be understood that the invention is not limited to these examples, but is susceptible to different modifications that will be recognized by one of ordinary skill in the art.

EXAMPLE 1 Composition percent weight Similar compositions are made employing any of the hereinbefore identified oxidants, fuels and gelling agents.

Results from performance calculations of the composition of Example 1 are listed below in Table I.

TABLE I Isp: 210 sec. Isp x density: 337 sec. x g./cc. Flame temperature: 3867 F. Freezing point: 25 C.

Density: 1.605 g./cc. at 25 C.

The amount of water soluble and condensable products produced upon combustiion of the composition of Example 1 is 98.3 volume percent. All of the combustion products are gaseous or liquid. Upon combustion in a Parr bomb under 400 p.s.i. helium pressure the energy released by the propellant of Example 1 is 1582 caL/g. as compared with a theoretical calculated value of 1486 cal/g.

The thermal stability of the composition of Example 1 is good. Differential thermal analysis shows an exotherm above 200 C., while no gas evolution was observed in a sample kept at 60 C. for 110 days.

The sensitivity characteristics of the formulation of Example 1 were determined by several methods. The results, summarized in Table II show that the gelled monopropellant has a very low level of sensitivity.

TABLE II Test: Result Card gap Zero cards. Cavity drop kg. x. cm. Bullet impact .Negative. Unconfined burning No detonation.

The gelled monopropellants of the present invention are non-Newtonian liquids which mean that the viscosity depends on the shear applied. As a general guideline, the apparent viscosity of a gelled liquid propellant should be below 100 poises. The results in Table III below show that the formulations of Examples 1 and 2 fulfill this requirement.

What is claimed and desired to be secured by Letters Patents of the United States is:

1. A gelled monopropellant composition comprising a mixture of water soluble oxidants, water, a water insoluble compatible fuel selected from the group consisting of boron, boron carbide, sulfur and phosphorus, and a gelling agent; wherein at least one oxidant is selected from the group consisting of metal chlorates, metal perchlorates, ammonium perchlorate, organic alkyl and aryl ammonium perchlorates, and at least one other oxidant is selected from the group consisting of hydroxylammonium perchlorate and other water soluble substituted hydroxylammonium perchlorates; and wherein the ratio of total oxidizer to water, by weight, is from about 7:1 to about 1:7 and the ratio of total oxidant to fuel varies from about 12:1 to about 1:8 and the gelling agent is present in amounts sufficient to keep the solid fuel in suspension.

2. The composition of claim 1 wherein the gelling agent is present from about 0.05 percent by weight to about 10 percent by weight of the total composition.

3. The composition of claim 2 wherein the gelling agent is present from about 0.5 percent to about 3 percent by weight of the total composition.

4. The composition of claim 1 wherein said other water soluble substituted hydroxylammonium perchlorates are selected from the group consisting of N-methyl hydroxylammonium perchlorate, N-ethyl hydroxylammonium perchlorate, O-methyl hydroxylammonium perchlorate and O-ethyl hydroxylammonium perchlorate; said metal chlorates are selected from the group consisting of lithium chlorate, sodium chlorate, magnesium chlorate, and aluminum chlorate; said metal perchlorates are selected from the group consisting of sodium perchlorate lithium perchlorate, magnesium perchlorate, potassium perchlorate, and aluminum perchlorate; and said organic alkyl and aryl ammonium perchlorate are selected from the group consisting of methylammonium perchlorate, methylene diammonium diperchlorate, ethylene diammonium diperchlorate and aniline perchlorate.

5. A composition according to claim 4 which comprises sodium perchlorate, hydroxylammonium perchlorate, boron, water and silica gel.

6. A composition according to claim 5 comprising, on a weight percent basis, 41.17 percent sodium perchlorate, 10.29 percent hydroxylammonium perchlorate, 11.64 percent boron powder, 33.98 percent water and 2.92 percent silica gel.

7. A composition according to claim comprising, on a Weight percent basis, 40.32 percent sodium perchlorate, 10.08 percent hydroxylammonium perchlorate, 33.28 percent boron powder, 11.36 percent water, and 4.96 percent silica gel.

8. The composition of claim 1 wherein said fuel is in a finely divided form.

9. The composition of claiml, wherein the quantity of fuel and total oxidant approximates the stoichiometric balance.

10. The composition of claim 1 wherein the ratio of oxidant selected from said group of hydroxylammonium perchlorate and other water soluble substituted hydroxylammonium perchlorates, to oxidant selected from said group consisting of sodiurn'perchlorate, metal chlorates, metal perchlorates. ammonium perchlorate and organic alkyl and aryl ammonium perchlorates, is about 1 to 4, by weight.

11. The composition of claim 1 wherein said mixture comprises sodium perchlorate and hydroxylammonium perchlorate.

12. The composition of claim 1 wherein said fuel is boron.

13. The composition of claim 1 wherein said gelling agent is silica gel.

References Cited UNITED STATES PATENTS 3,117,415 1/1964 Greene 35.4 3,305,413 2/1967 Flynn et al. 149-19 3,400,026 9/1968 Fearnow 14941 3,401,067 9/1968 Fee et al. 149-38 3,431,155 5/1969 Dunglinson et al. 14947 3,437,534 4/ 1969 McEwas et al 14930 3,457,126 7/1969 Travers et al. 149-2 3,523,841 8/1970 Knight 14921 CARL D. QUADFORTH, Primary Examiner E. A. MILLER, Assistant Examiner US. Cl. X.R. 

